Electrical actuation mechanism suitable for a disc brake assembly

Abstract

An improved structure for an electrical actuation mechanism adapted for use in a disc brake assembly includes an electrical actuation mechanism adapted to be secured to an inboard leg of the caliper of the disc brake assembly. The electrical actuation mechanism includes a housing, an electrical motor disposed in the housing, and a spindle disposed in the housing and operatively coupled to the motor by a conversion gear assembly which is effective to convert rotary motion generated by the motor into axial movement of the piston. The spindle includes a shaft and a piston which can be coupled to the shaft by a dampening structure. The shaft is operatively connected to the motor for axial motion thereof, and the piston is operatively connected to a friction pad for engaging a rotor attached to a wheel of a vehicle in which the disc brake assembly is installed. The dampening structure can be comprised of elastomeric material or a fluid filled chamber defined between the piston and the shaft. The dampening structure reduces the radial loads acted upon the piston from being transmitted to the shaft. The electrical actuation mechanism may also be equipped with sensors for sensing the axial position of the piston, a clutch, to couple and uncouple the electric motor from the conversion gear assembly, and a mechanism which prevents back drive motion of the electrical motor.

What is claimed is: 
     
       1. An apparatus comprising: a motor for imparting rotary motion; a shaft having a recess in one end;   a conversion gear assembly operatively connecting said motor to said shaft, said conversion gear assembly converting the rotary motion of said motor to axial motion of said shaft;   a piston having a projection disposed within said recess of said shaft; and   a dampening structure operatively connecting said projection on said piston to said shaft so that said piston can move relative to said shaft, said dampening structure dampening transmission of any radial force acting on said piston to said shaft, said dampening structure comprising a first elastomeric member circumferentially disposed about said projection and seated within an annular groove in said recess to resiliently and radially support said projection.     
     
     
       2. The apparatus of claim 1, wherein said projection has an end surface that is in contact with an end wall of said recess of said shaft.   
     
     
       3. The apparatus of claim 2, wherein said end surface of said projection and said end wall of said recess are generally flat.   
     
     
       4. The apparatus of claim 2, wherein said end wall of said recess is generally flat and said end surface of said projection is rounded. 
     
     
       5. The apparatus of claim 1, wherein said dampening structure includes a second elastomeric member engaging said shaft and said piston, and   compression of said first elastomeric member and second elastomeric member dampens transmission of radial forces acting on said piston to said shaft.   
     
     
       6. The apparatus of claim 1, wherein said conversion gear assembly includes: a spindle nut having internal threads, said spindle nut operatively connected to said motor; and   a plurality of planetary rollers each having formed on its outer surface first parallel grooves having a first pitch and second parallel grooves having a second pitch, where     said first pitch is greater than said second pitch,   said first parallel grooves engage said internal threads of said spindle nut, and   said second parallel grooves are engaged with external grooves formed on said shaft.   
     
     
       7. The apparatus of claim 1, wherein said piston is made of a phenolic material. 
     
     
       8. The apparatus of claim 1 incorporated into a disc brake assembly that comprises: a rotor adapted to be connected to a vehicle wheel for rotation therewith;   a caliper, operatively connected to said piston, said caliper comprising an inboard leg supporting an inboard friction pad,   an outboard leg supporting an outboard friction pad, and   an intermediate bridge portion interconnecting and supporting said inboard leg and said outboard leg in an operative position surrounding a portion of said rotor.     
     
     
       9. An apparatus comprising: a motor for imparting rotary motion;   a shaft;   a conversion gear assembly operatively connecting said motor to said shaft, said conversion gear assembly converting rotary motion of said motor to axial motion of said shaft;   a piston; and   a seal sealingly engaged with said shaft and said piston, said shaft, said piston, and said seal defining a fluid chamber capable of containing a constant volume of fluid, thereby coupling said piston to said shaft so that said piston can move relative to said shaft where said shaft further defines an opening providing communication through said shaft into said chamber, said apparatus further including a valve for selectively preventing fluid from escaping said fluid chamber through said opening.     
     
     
       10. The apparatus of claim 9 further including a source of fluid in fluid communication with said chamber through said opening such that fluid can be permitted to enter or exit said chamber through said valve. 
     
     
       11. The apparatus of claim 9, wherein said shaft has a recess formed therein, said piston include a projection disposed within said recess of said shaft, said recess, said projection and said seal defining said chamber. 
     
     
       12. The apparatus of claim 9, wherein said conversion gear assembly includes: a spindle nut having internal threads, said spindle nut operatively connected to said motor; and   a plurality of planetary rollers each having formed on its outer surface; first parallel grooves having a first pitch and   second parallel grooves having a second pitch, where     said first pitch is greater than said second pitch,   said first parallel grooves engage said internal threads of said spindle nut, and   said second parallel grooves are engaged with external grooves formed on said shaft.   
     
     
       13. The apparatus of claim 9 further including a disc brake assembly comprising: a rotor adapted to be connected to a vehicle wheel for rotation therewith;   a caliper including an inboard leg, an outboard leg, and an intermediate bridge portion; and   a friction pad operatively connected to said piston.   
     
     
       14. A disc brake assembly comprising: a rotor adapted to be connected to a vehicle wheel for rotation therewith;   a caliper including an inboard leg, an outboard leg, and an intermediate bridge portion;   an electrical actuation mechanism secured to said inboard leg of said caliper, said electrical actuation mechanism including a housing, an electrical motor disposed in said housing, and a spindle disposed in said housing and operatively coupled to said motor by a conversion gear assembly which is effective to convert rotary motion generated by said motor into axial movement of said spindle;   a sensor for sensing the rotation of said motor;   a clutch mechanism adapted to couple and uncouple said motor from said spindle by movement to, respectively, an engaged position and a disengaged position; and   a spring wrap brake for preventing movement of said spindle when said motor is not engaged, said spring wrap brake is movable between an engaged, position, wherein movement of said spindle is prevented, and a disengaged position, wherein movement of said spindle is permitted, said spring wrap brake operatively coupled to said motor through said clutch for movement to said disengaged position by rotating motion of said motor when said clutch is engaged.